This application claims the priority of Japanese Patent Application Nos. 3-284217 filed on Oct. 4, 1991 and 3-296270 and 3-296271 filed on Oct. 15, 1991, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an active autofocusing apparatus for measuring a subject distance in a camera by using a plurality of beams or one beam.
2. Description of the Related Art
In cameras, autofocusing control is executed by, for example, projecting multiple beams from a light emitting portion onto the object of photography and receiving the light reflected from the object by a light receiving portion. As shown in FIG. 16, a finder 2 and a lens barrel 4 holding a lens 3 are disposed on the front surface of a camera body 1, and an active light emitting portion (infrared light emitting diode) 5 for emitting infrared light and a light receiving portion 6 are disposed in a horizontal line. The light emitting portion 5 and the light receiving portion 6 measure the subject distance and outputs the autofocusing (AF) step number, as shown in FIGS. 17A and 17B.
In FIG. 17A, when beams are projected from the light emitting portion 5 onto the objects at different distances P.sub.1, P.sub.2, the beams reflected from the objects are received by a light receiving device 6B through a light receiving lens 6A. At this time, the light receiving device 6B receives the beam reflected from the object which is at a distance of P.sub.1 at a position p.sub.1, and the beam reflected from the object which is at a distance of P.sub.2 at a position p.sub.2, as shown in FIG. 17B. It is therefore possible to measure the subject distance from the position at which the beam is received by the light receiving device 6B. The AF step number which corresponds to the subject distance is allotted to the light receiving device 6B for the purpose of autofocusing control. The center 200 of gravity of the received beam (indicated by the broken line) 100 is first detected, and when the detected value is output from the light receiving device 6B as information on the measured subject distance, the AF step number is determined on the basis of the information. In this case, the light emitting portion 5 subsequently outputs three beams onto different positions of an object 7, as shown in FIGS. 18A and 18B, in order to accurately measure the subject distance. The AF step number is determined on the basis of these three beams, and the lens 3 is driven in accordance with the information on the AF step number, thereby focusing the lens 3 on the object 7.
In conventional autofocusing control by using multiple beams, however, when a projected beam is not completely impinged on the object 7 but is broken in the direction of the base length, as shown in FIG. 18A, the center of gravity of the beam changes, which causes an error in the measurement of the subject distance. More specifically, as shown in FIG. 17B, while the center of gravity of the beam 100 having a round section (indicated by the broken line) is situated at the position 200, the center of gravity of a beam 101 having a semicircular section (indicated by the solid line) deviates to the position 201. Therefore, although "n" should be output as the AF step number, "n-1" is actually output, so that autofocusing control becomes inaccurate.
FIG. 19 shows the AF step numbers output when one beam is projected and the camera body is swivelled by a predetermined angle. FIG. 20 shows the AF step numbers output when three beams are projected and the camera body is swivelled by a predetermined angle. In FIGS. 19 and 20, the portions A show the AF step numbers produced when there is no breakage of beam, and the portion B in which the AF step numbers are smaller (the subject distance is shorter) corresponds to the beam 101 in FIG. 17B, namely, the case in which the left side (the projected circle of the beam is reversed side to side by the projection lens) of the beam 101 is broken. The portion C in which the AF step number is larger (the subject distance is longer) is the case in which the right side of the beam is broken. In other words, the portions B and C in which the beam is broken are NG regions in which the lens 3 is out of focus. This is no problem when the object is in such a long distance that only one beam is projected onto the object 7, as shown in FIG. 18B, but becomes a problem when the object 7 is at such a short distance that at least two beams are impinged on the object 7, as shown in FIG. 18A. When there are at least two beam outputs, the smallest AF step number output is selected in a conventional autofocusing controlling apparatus. Especially, when the left side of a beam is broken, focus control is executed in the NG region shown by the portions B in FIG. 20.
Panoramic cameras for taking a photograph in a wide photographing range are conventionally known. There are panoramic cameras exclusively for panoramic photography and cameras which selectively enables both ordinary photography and panoramic photography. In a camera which enables both ordinary photography and panoramic photography by switching the photographing modes, a mask is set at the upper and lower portions of the exposing portion so as to cover the upper and lower portions of the film and an indicating frame which indicates the panoramic photography region is displayed in the finder in the panoramic photography mode.
In such a panoramic camera, autofocusing control is executed under an active system or the like using infrared light, ultrasonic waves, or the like. In the case of using infrared light, for example, infrared beams 110 (e.g., three beams) are projected onto the object 7 from the light emitting device, as shown in FIGS. 21A and 21B, so as to measure the subject distance, and the lens 3 is focused on the object 7 on the basis of the information on the measured subject distance.
In a conventional panoramic camera, however, the upper and lower portions of the photographed image of the object are sometimes missing. As shown in FIGS. 21A and 21B, an indicating frame 9 for indicating the panoramic photography region is displayed in a finder 8 in the panoramic photography mode but, sometimes, the indicating frame 9 is not utilized effectively. For example, although the indicating frame 9 is comparatively paid attention to immediately after the mode is changed over to the panoramic photography mode, while pictures are taken in the panoramic photography mode in combination with ordinary photography, the user may sometimes forget that the photographing mode is now the panoramic photography mode and take pictures without special attention to the indicating frame 9. In addition, the user may sometimes disregard the indicating frame 9 depending upon the photographing state although he is aware of the panoramic photography mode. If a picture is taken in the state shown in FIG. 21B in the panoramic photography mode for thee reasons, the head and the chin of the object are missing in the photographed image.
Furthermore, the indicating frame 9 displayed in the finder 8 may not be completely coincident with the actual panoramic photography region.
FIG. 22 shows an example of an autofocusing control circuit. In FIG. 22, a CPU (central processing unit) is 38 is connected to a subject distance measuring portion 37 which is composed of a light emitting device and a light receiving device, and a lens driving portion 39 is connected to the CPU 38. The CPU 38 executes the control of the camera as a whole and autofocusing control. The CPU 38 is provided therein, for example, with an AF step number setting portion 38A, a no-signal state detecting portion 38B and a lens movement control portion 38C. The camera is also provided with a panoramic photography button (not shown) for selecting the panoramic photography mode and a distant photography button (not shown) for selecting the distant photography mode.
According to this structure, when the panoramic photography mode is selected by pressing the panoramic photography button, for example, and a photography button is then pressed, autofocusing control is initiated. In the autofocusing control, the subject distance is measured on the basis of the state of the beam received by the light receiving device immediately after the control of the light emission from the light emitting device by the CPU 38, and when the information on the measured subject distance is output to the AF step number setting portion 38A, the AF step number for adjusting the focal length to the subject distance is output to the lens movement control portion 38C. When the lens driving portion 39 is driven by the lens movement control portion 38C, the photographing lens 3 is moved to a predetermined position, and the lens 3 is thereby automatically focused on the object 7.
In this circuit, the no-signal state detecting portion 38B detects that the beam reflected from the object 7 cannot be received by the light receiving device. When the no-signal state is detected, the lens 3 is so controlled as to be moved by a predetermined amount. In this type of camera, when the object 7 is situated at such a long distance as not less than several 10 m, the movement of the photographing lens 3 is generally controlled by a predetermined AF step number without receiving any reflected beam. In the above-described camera, the distant photography button is provided, and when the object 7 at a distance of not less than 100 m is photographed, the photographing lens 3 is so controlled as to focus on the distant object 7 not under autofocusing control but by pressing the distant photography button.
In a conventional camera which enables panoramic photography, however, the amount of lens movement (AF step number) set when the no-signal state is detected by the no-signal detecting portion 38B is appropriate in the ordinary photography mode but it is not always appropriate in the panoramic photography mode, which lead to a problem in the resolution of a picture. To state this more concretely, in panoramic photography for photographing a wide picture, the lens 3 is often focused on the object 7 at a comparatively long distance. In addition, in a panoramic camera, since a mask is generally disposed on the upper and lower portions of an ordinary film so as to take a picture while narrowing the vertical exposing range in the film, the enlargement ratio of the picture at the time of printing is larger than a picture taken in the ordinary photography mode. Therefore, if the amount of lens movement in the no-signal state in the panoramic photography mode is so set that the focal length is longer than that in the ordinary photography mode, it is possible to obtain a panoramic picture which is in focus.